BA shares are the top risers after US government preliminary approval for a tie-up with American Airlines. Photograph: Tim Ockenden/PA

The US government's decision to tentatively approve a tie-up between American Airlines, British Airways and other airlines has lifted shares in the UK carrier to the top of the FTSE 100's risers board this morning.

BA shares are up 8p, or 4.1%, at 203.5p in a FTSE 100 up around 40 points, or 0.8%, at 5183 at 10.20am UK time.

The move in BA's shares comes after the US Department of Transportation (DOT) gave its tentative approval this weekend to grant antitrust immunity to American Airlines and four "oneworld" alliance partners - British Airways, Iberia Airlines, Finnair and Royal Jordanian Airlines - to work more closely together.

It said in a statement that if its decision is made final the global alliance "would be able to more closely coordinate international operations in transatlantic markets."

It added:

"In today's show-cause order, the Department tentatively found that granting antitrust immunity to the oneworld alliance would provide travellers and shippers with a variety of benefits, including lower fares on more routes, increased services, better schedules and reduced travel and connection times. The Department also said the proposed alliance would enhance competition around the world by creating competition with the existing Star Alliance and the SkyTeam alliance, which already have been granted immunity."

On the other hand, the DOT also noted the alliance could "harm competition on select routes between the United States and London's Heathrow". So as a condition of approval, the DOT is proposing that the airlines make four pairs of slots available to competitors for new US-Heathrow services.

American Airlines says approval would level the playing field on business over the Atlantic, but Sir Richard Branson's Virgin Atlantic airline has already slammed the tie-up's regulatory progress, describing it as "a kick in the teeth" for consumers.

He said:

"The US Department of Justice, who are the experts in competition issues, called for strict remedies to protect the public interest, because the alliance will blatantly harm competition and the consumer. The Department of Transportation has chosen to stick two fingers up at them. Millions of transatlantic travellers will be adversely affected if the alliance receives final approval."